Everything You Need to Know About Injection Foam Wall Insulation

C.E. Larusso
Written by C.E. Larusso
Updated May 12, 2022
Living room decorated in Scandinavian style
Photo: FollowTheFlow / Adobe Stock


  • Injection foam fills closed cavities, making it perfect for retrofits.

  • The material forms a barrier to heat transfer and air leaks.

  • Installing injection foam requires a professional.

  • It’s the most expensive way to insulate your home.

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Few things are as important as reliable insulation when it comes to the enjoyment of your home. Insulation ensures that your rooms stay cool throughout the peak summer heat and toasty in the depths of winter. But if your existing insulation methods are starting to fail, driving up your energy bills, and keeping you under the blankets when you’d rather be out and about, injection foam could be just the retrofit solution you need. Foam insulation helps achieve energy-efficient comfort without breaking the bank—or a hole in your drywall.  

Here’s everything you need to know about injection foam, so you can decide whether or not it’s the best type of insulation for your home for you home.

What Is Injection Foam Insulation?    

Injection foam is a type of foam that expands much slower than spray foam, making it suitable to fill closed cavities. With a consistency like shaving cream, it’s—as the name implies—injected into walls through a small hole, filling up every space in the cavity, including hard-to-reach nooks and crannies between wiring and piping. 

Injection foam does not expand, so it can be fitted perfectly to any space without creating the kind of pressure that could crack or damage the walls. Because it can fill closed cavities, it’s a popular insulation replacement for older homes. If, however, you were previously using cellulose or other materials, contractors will need to clear as much out as possible before injecting the foam.

Pros and Cons of Injection Foam Insulation 

Insulation that's doing its job cuts down on thermal conduction (the transfer of heat or cold between surfaces) and convection (change in temperature due to airflow).

Injection foam insulation has a high R-value between R-4 and R-5 per inch, varying with the size of the cavity—the standard measure of resistance to thermal transfer. Foam really shines in offering protection against drafts and air leakage. While fiberglass and cellulose (the most common types of insulation) tend to settle and provide less protection over time, injection foam maintains its shape permanently. Since it does not sag or shrink away from the walls, it forms a highly effective air barrier that stops drafts in their tracks and prevents your cooled or heated air from escaping through cracks and electrical outlets. 

Air isn’t the only thing the foam barrier keeps out of your home; it also:

  • Reduces the amount of sound transfer from outside

  • Improves air quality by keeping out allergens

  • Works to slow the spread of smoke and fire 

  • Forms a barrier against moisture, reducing the growth of mold

In addition to enhancing comfort, injection foam insulation can save you money over time, help cut down on energy bills and boost your home’s ROI. 

Expect to spend between $0.44 and $6 per square foot, depending on the foam thickness. Add between $1.50 and $4.90 per square foot for professional installation.  

The Difference Between Injection and Spray Foam

Injection and spray foam are both designed with air sealing and thermal locking properties, but where they are used and their installation processes differ. 

Spray foam is composed of isocyanate and polyol resin, which react when mixed—creating an expanding foam that fills the area it’s applied to, which then hardens to create a seal. This seal protects against thermal transfer and air leakage. Spray foam is designed for use in open cavities and is most often applied in new builds and then covered with another material like drywall.        

Injection foam does not expand, making it suitable to fill closed cavities. It can be used to fill small areas and is often used in the nooks between pipes and wiring. Injection foam can be installed from your home’s exterior so you won’t need to open any walls or tear down any drywall.

How Injection Foam Insulation Is Installed

injecting insulation in to a brick wall
Photo: corlaffra / Adobe Stock

Suited perfectly for retrofits, injection foam insulation can be installed in existing homes without tearing down walls or leaving a big mess to clean up afterward.

Insulation contractors mix the formula on-site, typically in a truck connected to a nozzle. They usually install the material from the home's exterior. If you have aluminum or vinyl siding, the contractors will first remove a piece and drill holes into each wall's stud cavities. Typically working in a multi-person crew, the foreman will use the nozzle to fill each hole with the injection foam. Another crew member will follow behind to clean up any excess foam before it hardens. And a third crew member will clean up any drips or wood shavings that fall to the ground. Once a cavity is full, the foreman adds a styrofoam plug and reapplies the siding once the process is complete. 

The process is broadly similar to the other types of siding. The foam installation pro takes the following actions to seal up the area:

  • Brick: Contractors drill directly into mortar joints and then re-mortar and smooth it afterward.

  • Non-removable wood siding: Holes are filled with wood plugs instead of styrofoam. 

  • Concrete blocks: The foam fills the cavities of each block. 

In rarer cases, injection foam insulation installation happens inside the house. For example, if you have stone or slate walls that can’t be easily drilled, or if you’re only looking to add insulation to certain parts of the house. In situations like this, contractors will drill into the studs through your drywall, removing dust with a wet-dry vac and patching the holes with drywall mud after each stud cavity is full. Since the process is a little messier, it requires significantly more prep work, including moving furniture away from walls, covering unmovable features with plastic, and protecting the floors with sticky plastic or rosin paper.   

The whole installation typically takes between 3 to 5 hours, followed by a 24-hour period for the foam to harden.  

While there are DIY kits sold for small spray foam insulation projects, injection foam insulation should only be installed by an experienced foam insulation contractor. It's a difficult job that requires specialized equipment, and there are risks associated with improper installation—not only can poorly installed injection foam fail to provide adequate insulation, but the wrong mixture can also lead to off-gassing that can create serious health problems.

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